1. Field of the Invention
The present invention relates, in general, to a method for forming the sintered nickel electrodes which are used as cathodes in secondary alkaline batteries and, more particularly, to an improvement in property deviations among the nickel electrodes and in uniform battery properties as a result of the method.
2. Description of the Prior Art
Conventionally, nickel electrodes, which are used as cathodes in secondary alkaline batteries such as Ni-Cd batteries, Ni-Zn batteries, Ni-Fe batteries and Ni-MH batteries, are formed by immersing a porous nickel-sintered electrode plate in a nickel nitrate solution to form nickel hydroxide active materials within the nickel electrode plate, followed by the activation of the nickel hydroxide materials through formation processes comprising charging and discharging operations.
A conventional formation method is disclosed in U.S.S.R. Pat. No. 300,915, which relates to Ni-Zn batteries. In the U.S.S.R. patent, it is suggested that a nickel electrode and a zinc electrode are inserted in a cell, then having them be in the same discharged state by completely discharging them at the same time and, finally, charged them in such a way that the capacity of the zinc electrode may be larger than that of the nickel electrode.
As taught in the above-cited U.S.S.R. patent, a uniform electrode state through complete discharge could be accomplished and uniform battery properties and significant improvements in high rate discharge and low temperature properties could be effected. However, the formation method of the above-cited patent is disadvantageous in that a cellulose film, acting as a separator, is injured by oxidation attributable to the oxygen gas generated upon complete discharge of the zinc anode.
Another formation method of nickel electrode for alkaline secondary battery was suggested by M. A. Dasoyan in VYSHAYA SHKOLA p 387, 1970, in which nickel electrodes are discharged at an amount as large as the capacity thereof, followed by assembling the cell with the nickel electrodes and zinc electrodes and, finally by charging and discharging the cell. This formation method is preventive of the damage of a separator attributed to the gas generation in an electrode plate.
However, this conventional formation method is problematic in several aspects, as follows. A plurality of nickel electrode plates connected in parallel are treated to form nickel cathodes. Because there are differences in the amount of the active material among the nickel electrodes, the discharge states in each nickel electrodes become different after discharging up to an amount equal to the theoretical capacity of nickel electrodes. Thus, batteries employing such nickel electrodes do not have uniform properties. In particular, since extra capacity cannot be formed in the zinc electrode, a zinc powder should be separately added to the zinc electrode to secure the extra capacity. In addition, the formed extra capacity of the zinc electrode becomes nonuniform owing to the nonuniform properties of the nickel electrode. In result, if these batteries are applied in electric vehicles, the collective batteries cannot utilize enough battery properties as the operating state of each battery varies.